Comment 5 for bug 861351

This patch fixes the problem in the other one:
- a gtk3-compat.h file, which adds GDK_KEY_* and gtk_combo_box_text definitions for old gtk versions.
- --enable-gtk3 for waf (disable unique by default)
- extension building, statusbar-feature loading fail, because it uses a GtkComboboxEntry, which is not in gtk3 :(

I didn't test with a gtk version which doesn't have GDK_KEY*, so, I'm not 100% sure it works, but it should ^^ (if anyone would like to confirm me it works, the gtk version in ubuntu lucid doesn't have them).

Tell me if there is any problem :)